Unless otherwise indicated herein, the description in this section is not prior art to the claims in this application and is not admitted to be prior art by inclusion in this section.
As a typical method for calibration to perform correction of input-output characteristics, what is called, gamma correction caused by, for example, a secular change of an image forming apparatus such as a printer-only machine and a Multifunction Peripheral (MFP), there is known a method for measuring the current output color using a scanner attached to the MFP or a print density sensor inside the image forming apparatus to correct the input-output characteristics such that the color value of the output color becomes a target color value.
However, mutual coordination of the color values of the output colors between image forming apparatuses as different models requires an expensive dedicated colorimeter such as a spectrophotometric colorimeter. However, to prepare and master the dedicated colorimeter, it is difficult for a general user.
Therefore, there is proposed a calibration system that realizes simple and low-cost calibration by using an photographing device such as a digital camera and a mobile phone with a camera as an alternate device of the dedicated colorimeter.
In one calibration system, firstly, a reference chart including patches in a plurality of colors and a test chart printed by an image forming apparatus corresponding to the reference chart are simultaneously photographed by an photographing device. The, the tone characteristics of the image forming apparatus is corrected based on the RGB values of the respective patches of the reference chart and the test chart in the image, which is photographed and generated by the photographing device.
In another calibration system, firstly, a reference chart including patches in a plurality of colors and a test chart printed by an image forming apparatus corresponding to the reference chart are separately photographed by an photographing device. Subsequently, a first correction value is calculated based on: the color value of the patch of the reference chart in the first image, which is photographed and generated by the photographing device; and the color value of the patch of the test chart in the second image, which is photographed and generated by the photographing device. Additionally, a second correction value is calculated based on: the color value of the patch of the reference chart in the first image, which is photographed and generated by the photographing device; and the color value of the reference preliminarily stored in the image forming apparatus. Then, the tone characteristics of the image forming apparatus are corrected based on the first correction value and the second correction value.